JP2008066444A - Method of manufacturing wiring circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To fill a through-hole without generating air bubbles. <P>SOLUTION: A first back-surface-side resin film 31 is applied onto the back side of a substrate 11a; a through-hole 22 is filled with the first back-surface-side resin film 31 to midway of the hole in its depth direction to form a semi-filled hole 28; the surface of the semi-filled hole is coated with a photosensitive resin solution to form a photosensitive resin film 26 and to fill the semi-filled hole 28; then the photosensitive resin film is patterned to form a filler 27 within the semi-filled hole 28. Since the through-hole 22 is filled down to a shallow level of the depth thereof, this can avoid entrainment of any air bubbles. A cover film is provided apart from the filler 27, and the filler 27 and a wiring film 24a are covered with the cover film. In this way, the thickness of the photosensitive resin film 26 is reduced, so that the photosensitive resin solution have a low viscosity. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a wiring board, and more particularly to a flexible wiring board for double-sided wiring.

Various types of flexible wiring boards have been developed in response to demands for smaller and lighter electronic devices.
Among them, the double-sided flexible wiring board is important as a circuit board for small devices because wiring between mounted circuit components is easy and the area can be saved.

  The wiring film on the front surface of the double-sided flexible wiring board and the wiring film on the back surface are electrically connected by a through hole. A cover film is formed on the surface of the wiring film and insulated, and the through hole is filled with resin. Techniques for improving the strength and reliability of the wiring board are important.

A low-viscosity resin is desirable for filling the through hole with resin, and a high-viscosity paste-like resin is applied to increase the film thickness in order to form a cover film that protects the wiring film. And curing.
Various flexible wiring board manufacturing methods have been proposed, and the following documents are given as an example.
JP 58-124293 A JP-A-2-90697 Japanese Patent Laid-Open No. 3-236156 JP-A-6-69631

In order to fill the through hole and protect the wiring film with a thick cover film, the following manufacturing method was first developed.
The manufacturing method will be described with reference to FIG. 3A. Reference numeral 111 denotes a substrate in a state where the plating process is completed. The inner peripheral surface of the through hole formed in the base film 121 is plated by a plating method. A connection layer 123 made of the grown copper thin film is disposed, and a through hole 122 is formed by the through hole and the connection layer 123.
Wiring films 124 a and 124 b are respectively disposed on both surfaces of the base film 121, and the wiring films 124 a and 124 b on both surfaces are connected by a through hole 122.

In this state, the surfaces of the wiring films 124a and 124b are exposed, and first, the substrate 111 is placed on the work table with the back surface facing the work table so as not to be short-circuited by contact with other components or electronic circuits. Then, a photosensitive resin solution is applied, and the inside of the through hole 122 is filled with the photosensitive resin solution. At this time, the photosensitive resin liquid is also applied to the wiring film 124 a on the surface side of the substrate 111.
It is dried in that state, and a photosensitive resin film 126 is formed as shown in FIG.
The photosensitive resin liquid has a low viscosity because it fills the fine through-hole 122, and the film thickness of the photosensitive resin film 126 on the wiring film 124a becomes thin.

  Therefore, the photosensitive resin film 126 is patterned once by exposure and development to form a patterned photosensitive resin film 127 that covers the through hole 122 as shown in FIG. Other portions are removed during development, and the surface side wiring film 124a is exposed.

  Next, as shown in FIG. 3 (d), after forming a cover film 134 made of a photosensitive resin on the surface of the substrate 111, the cover film 134 is patterned by exposure and development, as shown in FIG. 3 (e). Then, a patterned cover film 135 is disposed on the wiring film 124a.

  Then, as shown in FIG. 5F, a cover film 132 is also arranged on the back surface side, and after patterning as necessary, the substrate 111 is heated, and the photosensitive resin film 127 and the front and back cover films 135 are heated. , 132 is cured, the double-sided flexible wiring board 112 in which the wiring films 124a, 124b are protected by the cover films 135, 132 and the through holes are filled with the photosensitive resin film 127 is obtained.

  However, in the manufacturing method as described above, when the through hole 122 is miniaturized and the aspect ratio of the through hole is increased, air is entrained in the through hole 122 when the photosensitive resin liquid is applied to fill the through hole 122. There is a disadvantage that bubbles 130 are generated in the through holes 122.

  When the bubble 130 is generated, the circuit is disconnected due to the burst of the bubble at the time of reflow, or the resist is peeled off to cause a short circuit, which causes a decrease in the connection reliability of the circuit of the double-sided flexible wiring board 112.

  Further, when the photosensitive resin liquid is applied to the front surface side of the substrate 111 and the through hole 122 is filled, the resin liquid that may have passed through the through hole 122 oozes out to the back surface side of the substrate 111 and is placed on the platform on which the substrate 111 is placed When the photosensitive resin liquid adheres, there is a problem that other substrates are contaminated.

In order to solve the above problems, the present invention provides a base film, a first wiring film disposed on the surface of the base film, a second wiring film disposed on the back surface of the base film, and the base film. A first back side resin film is pasted on the back side of the wiring board having a through hole electrically connecting the first and second wiring films, and the first back side resin film The through hole is filled in the middle of the thickness direction to form a semi-filled hole, a photosensitive resin liquid having fluidity is applied to the surface side of the wiring board, and the semi-filled hole is filled with the photosensitive resin liquid. It is a manufacturing method of a wiring board which forms a photosensitive resin film from the photosensitive resin liquid in a filled state.
Further, according to the present invention, the thickness of the first back surface side resin film fitted in the through hole is in the range of 30% to 70% of the depth of the through hole. It is a manufacturing method of a wiring board.
In the present invention, the thickness H of the photosensitive resin film on the first back-side resin film on the bottom surface of the half-filling hole is larger than the depth d of the half-filling hole, and the through hole This is a method of manufacturing a wiring board that is smaller than the depth D.
Moreover, this invention is a manufacturing method of the wiring board which patterns the said photosensitive resin film to predetermined plane shape by exposure and image development.
Moreover, this invention is a manufacturing method of the wiring board which covers the said photosensitive resin film patterned with the protective film.
Moreover, this invention is a manufacturing method of the wiring board which arrange | positions a 2nd back surface side resin film on the back surface side of the said wiring board after etching-removing said 1st back surface side resin film.
Moreover, this invention is a manufacturing method of the wiring board which etches away the said 1st back surface side resin film with a developing solution, when developing the said photosensitive resin film.

  Since the deep through hole is filled from the back side to the middle in the depth direction with the first back side resin film to form a shallow half-filled hole and fill the half-filled hole, no bubbles are generated. Further, even during filling, the photosensitive resin liquid does not ooze out to the back side and does not contaminate other substrates.

  Moreover, since the cover film which covers the wiring film and the photosensitive resin film on the through hole is provided separately from the photosensitive resin film, the thermal history of the cover film is small and the etching accuracy can be increased.

  Further, since the thickness on the wiring film 24a outside the through hole of the photosensitive resin liquid and the thickness on the base film 21 can be made smaller than the depth D of the through hole, patterning of the photosensitive resin film is easy.

  Referring to FIG. 1, reference numeral 11 a in FIG. 1A is a substrate that can be used in the present invention, and has a base film 21. Wiring films 24a and 24b are formed on the front and back surfaces of the base film 21, respectively.

  The base film 21 is a resin film such as polyimide, and the wiring films 24a and 24b are formed by patterning a copper foil by etching. The base film 21 and the wiring films 24a and 24b have a thickness of several μm to several tens of μm, are flexible, and are configured such that the substrate 11a has flexibility.

  The base film 21 has a through hole penetrating the base film 21 in the thickness direction. A conductive connection layer 23 is formed on the inner peripheral surface of the through hole by a plating method to connect to the through hole. Through hole 22 is formed by layer 23. The connection layer 23 can be formed, for example, by depositing copper.

  The wiring film 24 a on the front surface of the base film 21 and the wiring film 24 b on the back surface are connected to the connection layer 23, and the wiring films 24 a and 24 b on the front surface and the back surface of the base film 21 are electrically connected by the through holes 22. It is connected. The symbol D in FIG. 6A represents the depth of the through hole 22 and is a total value of the thickness of the base film 21 and the thicknesses of the wiring films 24a and 24b on the front and back surfaces.

Next, as shown in FIG. 4B, the back surface of the substrate 11a is brought into close contact with the first back surface resin film 31 having adhesiveness and pressed to the back surface of the substrate 11a. A film 31 is attached.
At this time, the substrate 11 a and the first back surface side resin film 31 are pressed, and the surface of the first back surface side resin film 31 is inserted into the through hole 22. Reference numeral 11b in FIG. 5B shows the substrate in this state.
The pressing amount and the pressing force are controlled, and the first back surface side resin film 31 is fitted into the through hole 22 partway in the thickness direction to form the half filling hole 28.

The thickness t of the portion inserted into the through hole 22 is not limited, but it is preferable that the thickness t be equal to or greater than at least the thickness of the wiring film 24b on the back surface side and be surely positioned inside the base film 22.
In order to prevent bubbles from being formed when the half-filling hole 28 is filled later, the thickness t to be inserted into the through hole 22 is in the range of 30% to 70% of the depth D of the through hole. That is, it is desirable to set it in the range of D / 2 ± D × 20%.
The semi-filling hole 28 in this state has the bottom surface exposed at the tip of the fitting portion of the first back-side resin film 31, and the depth d of the semi-filling hole 28 is a size of D−t.

  Next, when the surface of the substrate 11b is directed upward and the first photosensitive resin liquid is applied in a region including the half filling hole 28, the half filling hole in which the surface of the first back side resin film 31 is exposed on the bottom surface. 28 is filled. The bottom surface of the through hole 22 in which the half filling hole 28 is formed is closed by the first back side resin film 31, and the first photosensitive resin liquid applied in the half filling hole 28 is formed on the substrate 11b. There is no leakage to the back side.

  A plurality of through-holes 22 are formed, and when one first back-side resin film 31 is attached to the back surface, a plurality of half-filling holes 28 are formed together. For the plurality of half-filling holes 28, the first photosensitive resin liquid may be applied to the entire surface of the substrate 11 to fill the plurality of half-filling holes 28 together. You may apply | coat partially for every area | region containing the filling hole 28. FIG.

When the applied first photosensitive resin liquid is dried, the first photosensitive resin liquid is turned into a film, and a substrate 11c on which the photosensitive resin film 26 is formed is obtained as shown in FIG.
Here, when the first photosensitive resin liquid is applied onto the substrate 11b, the surface of the first back-side resin film 31 is exposed on the bottom surface of the half-filling hole 28, and the applied first The thickness H of the photosensitive resin liquid on the first back-side resin film 31 located on the bottom surface of the half-filling hole 28 is larger than the depth d of the half-filling hole 28. The connection layer 23 on the peripheral surface and the wiring film 24a around the opening are not exposed.

The thickness H is larger than the depth d of the half-filling hole 28 (d <H) in order to fill the entire half-filling hole 28 in the depth direction. Assuming that the thickness of the photosensitive resin film 26 formed by drying is equal to the thickness H on the bottom surface of the half-filling hole 28 of the applied first photosensitive resin liquid, it is positioned at the opening of the half-filling hole 28. The connecting layer 23 and the wiring film 24a to be formed are covered with the photosensitive resin film 26, but it is desirable that the connecting layer 23 and the wiring film 24a be applied thinly so as not to entrap bubbles and to be easily patterned.
As the first photosensitive resin liquid to be applied, a liquid having a lower viscosity and higher fluidity than a resin paste for a cover film, which will be described later, can be used so as to flow into the fine half-filled holes 28.

In the case where the through hole is completely filled in the depth direction without forming the half filling hole, the first photosensitive resin liquid needs to be applied and applied thicker than the depth D of the through hole. On the other hand, in the present invention, the through-hole 22 at the time of application is made into a shallow half-filling hole 28 by the first back-side resin film 31, and the first photosensitive resin liquid only needs to fill the half-filling hole 28. The film thickness H of the coating layer of the first photosensitive resin liquid can be made thinner (H <D) than the case where the through hole is filled. As will be described later, the first photosensitive resin liquid is desirably coated flat on the surface in order to pattern the photosensitive resin film 26 by exposure and development.
When the photosensitive resin film 26 is thinned, patterning is easy, but it is insufficient to use as a cover film for the wiring film 24a.

In this invention, the mask which has a light-shielding part and a translucent part is arrange | positioned on the photosensitive resin film 26, and the photosensitive resin film 26 is patterned by exposure and image development.
When the photosensitive resin film 26 is a photocurable resin, the portion irradiated with the exposure light that has passed through the light transmitting portion is cured, becomes insoluble in the developer, and the portion that is not irradiated with the exposure light is cured. Without dissolving in the developer. When the photosensitive resin film 26 is a photodegradable resin, the portion irradiated with the exposure light transmitted through the light transmitting portion is decomposed, becomes soluble in the developer, and the portion where the exposure light is not irradiated at the light shielding portion. It does not decompose and remains insoluble in the developer.

  Regardless of the type of resin, the photosensitive resin film 26 is patterned by exposure and development to form at least a filling portion 27 composed of the remaining portion of the photosensitive resin film 26 as shown in FIG. Then, the inside of the half filling hole 28 is filled by the filling portion 27. Here, the connection layer 23 located at the opening of the half-filling hole 28 and the wiring film 24a in the vicinity thereof are also left. Reference numeral 11d in FIG. 6D shows the substrate in this state.

  The first back side resin film 31 is a resin that dissolves in a developer that dissolves the soluble portion of the photosensitive resin film 26, and the first back side resin film 31 is used when developing the photosensitive resin film 26. When the photosensitive resin film 26 is patterned, the first back side resin film 31 in the through hole 22 is also removed, and the back side of the substrate 11d is exposed including the back side of the through hole 22, On the back surface side, a shallow hole 29 in which the filling portion 27 is located on the bottom surface is formed. The wiring film 24a and the base film 21 are exposed on the surface side.

The first backside resin film 31 may be peeled off after exposing and developing the photosensitive resin film 26 using a resin that is not etched by the developer of the photosensitive resin film 26. Since there is a possibility of damaging the wiring film 24b, it is desirable to etch away together with the soluble portion of the photosensitive resin film 26 when developing the photosensitive resin film 26.
The first back side resin film 31 is a photosensitive acrylic resin film, and the photosensitive resin film 26 is a photosensitive epoxy resin. The developer is an alkaline solution.

Next, when a second photosensitive resin liquid made of the same type of resin as the first photosensitive resin liquid of the photosensitive resin film 26 is applied to the surface of the substrate 11d and dried, a photosensitive cover film 34 is formed. Is done.
Reference numeral 11e in FIG. 2 (e) denotes a substrate on which the cover film 34 is formed. The cover film 34 has a film thickness that covers the filling portion 27 that covers the through hole 22. The surface of the cover film 34 is formed flat.

  The second photosensitive resin liquid for forming the cover film 34 does not need to be filled with fine through holes, and has a higher viscosity than the photosensitive resin liquid on which the photosensitive resin film 26 in FIG. 1C is formed. Can be used. The film thickness of the cover film 34 can be made thicker than the film thickness on the wiring film 24 a of the photosensitive resin film 26.

If the cover film 34 is formed without patterning the photosensitive resin film 26 and the photosensitive resin film 26 and the cover film 34 are to be patterned together, the photosensitive resin film 26 is heated twice before patterning. It will be processed and fine patterning will not be possible. Therefore, it is desirable to pattern the photosensitive resin film 26 before applying the second photosensitive resin liquid.
When a mask is placed on the cover film 34, exposed, developed, and patterned, a substrate 11f having a patterned cover film 35 is obtained as shown in FIG.

Next, as shown in FIG. 5G, a resin liquid is applied to the back surface side of the substrate 11f, the shallow holes 29 are filled with the resin liquid, and dried in this state to form a resin film 32 that covers the back surface. To do.
Next, when the resin film 32 is patterned by exposure and development and cured by heat treatment, a second back side resin film 33 is formed as shown in FIG. Reference numeral 12 in FIG. 2H denotes the wiring board 12 in this state.

The filling portion 27 and the cover film 35 are cured together when the second back surface resin film 33 is cured.
The base film 21, the wiring films 24 a and 24 b, the filling portion 27, the cover film 35, and the second back side resin film 33 of the wiring board 12 have flexibility, and therefore the wiring board 12 can be bent. Flexible.

  In addition, the said photosensitive resin liquid includes a paste-like thing besides a liquid form. Each film may be heat-cured together, or may be individually heat-cured after patterning.

(a)-(d): The figure for demonstrating the wiring board manufacturing method of this invention (e)-(h): The figure for demonstrating the wiring board manufacturing method of this invention (a)-(f): The figure for demonstrating the wiring board manufacturing method relevant to this invention

Explanation of symbols

11a to 11g ... substrate 12 ... wiring substrate 21 ... base film 22 ... through holes 24a, 24b ... first and second wiring films 26 ... photosensitive resin film 27 ... filling portion 31 ... first One back-side resin film 33 ... second back-side resin film D ... depth of through hole in a state where the inside is not filled d ... the inside is halfway in the depth direction by the first back-side resin film Depth of filled through hole H ... Thickness of photosensitive resin film in through hole

Claims (7)

A base film,
A first wiring film disposed on the surface of the base film;
A second wiring film disposed on the back surface of the base film;
A first back side resin film is attached to the back side of the wiring board having a through hole that penetrates the base film and electrically connects the first and second wiring films, and the first back side Filling the through hole partway through the thickness direction with the side resin film to form a half-filled hole,
A wiring board that forms a photosensitive resin film from the photosensitive resin liquid in a state in which a photosensitive resin liquid having fluidity is applied to the surface side of the wiring board and the semi-filled holes are filled with the photosensitive resin liquid. Manufacturing method.   2. The wiring according to claim 1, wherein a thickness of the first back surface side resin film fitted in the through hole is in a range of 30% to 70% of a depth of the through hole. A method for manufacturing a substrate.   The thickness H of the photosensitive resin film on the first back-side resin film on the bottom surface of the half-filling hole is larger than the depth d of the half-filling hole and is larger than the depth D of the through-hole. The method for manufacturing a wiring board according to claim 1, wherein the wiring board is made smaller.   The method for manufacturing a wiring board according to claim 1, wherein the photosensitive resin film is patterned into a predetermined planar shape by exposure and development.   The manufacturing method of the wiring board of Claim 4 which covers the patterned said photosensitive resin film with a protective film.   6. The method of manufacturing a wiring board according to claim 4, wherein after the first back side resin film is removed by etching, a second back side resin film is disposed on the back side of the wiring board. 7. .   The method for manufacturing a wiring board according to claim 6, wherein the first back side resin film is removed by etching with a developer when the photosensitive resin film is developed.

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